I have spent countless hours trying to find a cheap way to get my ipod connected to my radio with a very good quality link. FM modulators suck, you know all about it. I have heard a lot from others online too. This is my cheap fix that might work with yours too, and im pretty sure that all the interfaces are the same for the internal 1-CD player. Cd changers are even easier and I think I saw a demo for that before too.

TOOLS NEEDED: soldering iron, wire strippers(your teeth...jk), screwdriver
ITEMS NEEDED: long extension cable for headphones, you will be cutting one end off.
if you can find in your garage or somewhere a headphone (male) coupling with an open end, then you are lucky and you don't have to buy one. I just got mine from radioshack its quality and the wires are big and easy to solder.
Sometimes headphone wires will be small and enamel-coated (instead of insulated rubber) and they can be tricky so don't use them unless you are zuper awezome.
SKILLS REQ'D : soldering, understanding your own car's components, understanding basic radio components and being comfortable altering them.

I have pictures from my radio, and you can see how it was done from the pictures I took after I finished and was putting it back together.
It depends on which radio you have, I have the A51813 well thats what it says on the outside
A51813
Model No. 816120-02430
Ref No. CQ-JS7460X
Serial No. MX658147

Step 1: Take the Radio Out

I have seen other places showing how to take the radio out but all you have to do is take the shifter cover out, you can pry it from the back a little and the front a little and it will come out.
Taking off the heater and shelf middle console only has one screw which is in the center knob(the fan speed).
Taking out the vent part is easy if you shove your fingers on the sides and push while you pry a little.
Main point - Get the radio out
Once the radio's surroundings are removed, it is easy to unscrew the 4 bolts underneath with a long tool that fits and when taking it out or putting it in, you must go straight and slow and pay attention to where it is going, maybe use a flashlight if you can't see inside. Mine had 6 holes because two of the screw sites had additional holes where a plastic spike went. Keep track of the screws because the next step has many more.

Step 2: The Radio Dissasembly

There are 3 different type of screws. The first are the huge ones for the side harness, take those out first and put the harnesses aside.
The next are the little metal to metal screws, those are the majority.
There is also one more metal to metal screw, but it is for the cd drive, and there are two screws that look different from all the rest. They are different sizes, and need to be put in the right hole.
There are a couple screws on the sides of the radio, on the top of the radio, and on the back there are about 6 that are connected to the metal outer shell. take all of them out and the top part that says open should be opened first, then the sides, which slide straight up.
The cd part is loose and should slide straight up out.
-Be careful with the cable, and unplug it. The images are of it after I soldered the wires, but you can stil see how it fits together.
I used a long headphone jack I got from radioshack and cut it to my desired length and stripped the wires. I played around to get the right ones, and the solder points are circled in the pic.

Step 3: Put It Back In

Put everything back the same way it went in.
The cd screws are the lighter looking ones.
If you want to play a cd, make sure the ipod is unplugged.
If you want to listen to ipod, just put a cd in there upside down, it will read error, but the ipod can still play.

If you have any questions just ask